GB2523762A - Active compensation of magnetic field generated by a recondensing refrigerator - Google Patents

Active compensation of magnetic field generated by a recondensing refrigerator Download PDF

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Publication number
GB2523762A
GB2523762A GB1403757.6A GB201403757A GB2523762A GB 2523762 A GB2523762 A GB 2523762A GB 201403757 A GB201403757 A GB 201403757A GB 2523762 A GB2523762 A GB 2523762A
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GB
United Kingdom
Prior art keywords
displacer
cryogenic
refrigerator
magnetic
cryogenic refrigerator
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
GB1403757.6A
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GB201403757D0 (en
Inventor
Marcel Jan Marie Kruip
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Siemens PLC
Original Assignee
Siemens PLC
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Siemens PLC filed Critical Siemens PLC
Priority to GB1403757.6A priority Critical patent/GB2523762A/en
Publication of GB201403757D0 publication Critical patent/GB201403757D0/en
Priority to PCT/EP2015/052868 priority patent/WO2015132055A1/en
Priority to EP15705950.2A priority patent/EP3114494A1/en
Publication of GB2523762A publication Critical patent/GB2523762A/en
Withdrawn legal-status Critical Current

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Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R33/00—Arrangements or instruments for measuring magnetic variables
    • G01R33/20—Arrangements or instruments for measuring magnetic variables involving magnetic resonance
    • G01R33/28—Details of apparatus provided for in groups G01R33/44 - G01R33/64
    • G01R33/38—Systems for generation, homogenisation or stabilisation of the main or gradient magnetic field
    • G01R33/3804—Additional hardware for cooling or heating of the magnet assembly, for housing a cooled or heated part of the magnet assembly or for temperature control of the magnet assembly
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25D—REFRIGERATORS; COLD ROOMS; ICE-BOXES; COOLING OR FREEZING APPARATUS NOT OTHERWISE PROVIDED FOR
    • F25D19/00—Arrangement or mounting of refrigeration units with respect to devices or objects to be refrigerated, e.g. infrared detectors
    • F25D19/04—Arrangement or mounting of refrigeration units with respect to devices or objects to be refrigerated, e.g. infrared detectors with more than one refrigeration unit
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25D—REFRIGERATORS; COLD ROOMS; ICE-BOXES; COOLING OR FREEZING APPARATUS NOT OTHERWISE PROVIDED FOR
    • F25D29/00—Arrangement or mounting of control or safety devices
    • F25D29/001—Arrangement or mounting of control or safety devices for cryogenic fluid systems
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R33/00—Arrangements or instruments for measuring magnetic variables
    • G01R33/20—Arrangements or instruments for measuring magnetic variables involving magnetic resonance
    • G01R33/28—Details of apparatus provided for in groups G01R33/44 - G01R33/64
    • G01R33/38—Systems for generation, homogenisation or stabilisation of the main or gradient magnetic field
    • G01R33/381—Systems for generation, homogenisation or stabilisation of the main or gradient magnetic field using electromagnets
    • G01R33/3815—Systems for generation, homogenisation or stabilisation of the main or gradient magnetic field using electromagnets with superconducting coils, e.g. power supply therefor
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R33/00—Arrangements or instruments for measuring magnetic variables
    • G01R33/20—Arrangements or instruments for measuring magnetic variables involving magnetic resonance
    • G01R33/28—Details of apparatus provided for in groups G01R33/44 - G01R33/64
    • G01R33/38—Systems for generation, homogenisation or stabilisation of the main or gradient magnetic field
    • G01R33/387—Compensation of inhomogeneities
    • G01R33/3873—Compensation of inhomogeneities using ferromagnetic bodies ; Passive shimming
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R33/00—Arrangements or instruments for measuring magnetic variables
    • G01R33/20—Arrangements or instruments for measuring magnetic variables involving magnetic resonance
    • G01R33/28—Details of apparatus provided for in groups G01R33/44 - G01R33/64
    • G01R33/38—Systems for generation, homogenisation or stabilisation of the main or gradient magnetic field
    • G01R33/387—Compensation of inhomogeneities
    • G01R33/3875—Compensation of inhomogeneities using correction coil assemblies, e.g. active shimming
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R33/00—Arrangements or instruments for measuring magnetic variables
    • G01R33/20—Arrangements or instruments for measuring magnetic variables involving magnetic resonance
    • G01R33/28—Details of apparatus provided for in groups G01R33/44 - G01R33/64
    • G01R33/42—Screening
    • G01R33/421—Screening of main or gradient magnetic field
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
    • H01F6/00—Superconducting magnets; Superconducting coils
    • H01F6/04—Cooling
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25B—REFRIGERATION MACHINES, PLANTS OR SYSTEMS; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS
    • F25B9/00—Compression machines, plants or systems, in which the refrigerant is air or other gas of low boiling point
    • F25B9/10—Compression machines, plants or systems, in which the refrigerant is air or other gas of low boiling point with several cooling stages
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25B—REFRIGERATION MACHINES, PLANTS OR SYSTEMS; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS
    • F25B9/00—Compression machines, plants or systems, in which the refrigerant is air or other gas of low boiling point
    • F25B9/14—Compression machines, plants or systems, in which the refrigerant is air or other gas of low boiling point characterised by the cycle used, e.g. Stirling cycle
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R33/00—Arrangements or instruments for measuring magnetic variables
    • G01R33/20—Arrangements or instruments for measuring magnetic variables involving magnetic resonance
    • G01R33/44—Arrangements or instruments for measuring magnetic variables involving magnetic resonance using nuclear magnetic resonance [NMR]
    • G01R33/48—NMR imaging systems
    • G01R33/54—Signal processing systems, e.g. using pulse sequences ; Generation or control of pulse sequences; Operator console
    • G01R33/56—Image enhancement or correction, e.g. subtraction or averaging techniques, e.g. improvement of signal-to-noise ratio and resolution
    • G01R33/565—Correction of image distortions, e.g. due to magnetic field inhomogeneities
    • G01R33/56563—Correction of image distortions, e.g. due to magnetic field inhomogeneities caused by a distortion of the main magnetic field B0, e.g. temporal variation of the magnitude or spatial inhomogeneity of B0

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  • Physics & Mathematics (AREA)
  • Engineering & Computer Science (AREA)
  • General Physics & Mathematics (AREA)
  • Condensed Matter Physics & Semiconductors (AREA)
  • Combustion & Propulsion (AREA)
  • Chemical & Material Sciences (AREA)
  • Mechanical Engineering (AREA)
  • Thermal Sciences (AREA)
  • General Engineering & Computer Science (AREA)
  • Magnetic Resonance Imaging Apparatus (AREA)
  • Epidemiology (AREA)
  • Health & Medical Sciences (AREA)
  • Electromagnetism (AREA)
  • Power Engineering (AREA)

Abstract

A magnetic resonance imaging apparatus has a compensating magnetic field cancelling a disturbing magnetic field generated by a displacer in a cryogenic refrigerator (1). Examples include active correction coils, synchronised operation of at least two refrigerators (1) in a given phase relationship, and a magnetic body (4) mounted on a rotating crank (5)

Description

Description
Active compensation of magnetic field generated by a recondensing refrigerator
Technical Field
The invention relates to a cryogenic refrigerator having a movable displacer, a cryogenic refrigerator arrangement including a plurality of cryogenic refrigerators and a magnetic resonance imaging apparatus including such a cryogenic refrigerator or such a cryogenic refrigerator arrangement.
Technical Background
Cryogenic refrigerators with a second stage temperature of less than 4.2 Kelvin are routinely used to cool superconducting magnets. The most wide-spread application of such magnets are Magnetic Resonance Tmaging (MRT) scanners.
The commonly used refrigerators are Gifford-MacMahon refrigerators including two cooling stages. The second stage comprises a displacer which moves in a cyclical fashion within a receptacle thereby displacing cold gas between opposite ends of the receptacle. This displacer is commonly made of a material having a high thermal capacity such as Holmium Copper (HoCu) . Unfortunately these materials also have magnetic properties which cause them to be magnetised by external magnetic fields such as a stray field in the vicinity of an MRS magnet. Since the refrigerator needs to be mounted in proximity to the magnet, the stray field will magnetise the displacer and the displacer will thus, in good approximation, behave like a dipole. As the displacer moves during operation of the refrigerator with a typical amplitude of about 35 millimetres, a field variation caused by the magnetised displacer can affect the image quality of the MRI scanner. This is because the angle between the line connecting the centre cf the displacer to the centre of the magnet arid the line along which the displacer moves does not equal 90 degrees.
This problem has been mitigated as proposed in US 7,196,600 B2 by using a shield arranged around the second stage of the refrigerator and made of a meta material. However, the effectiveness of this approach is limited by the fact that the shield cannot enclose the refrigerator completely to the effect that oscillating magnetic flux may still leak from the refrigerator.
JP2009061010A proposes tilting the refrigerator in such a way that the displacer of the refrigerator moves vertically in respect to the line between the refrigerator and the centre of the magnet. However, such an arrangement of the refrigerator is disadvantageous because the refrigerator works optimally when oriented vertically. Furthermore the bottom of the refrigerator should be located above the fill level of the liquid helium used for cooling. Thus, the effectiveness of the refrigerator will be affected when tilted.
Accordingly it is an object of the invention to provide an enhanced cryogenic refrigerator, an enhanced cryogenic refrigerator arrangement and an enhanced MRI apparatus.
Sununary of the Invention To achieve the aforegoing objective, a first aspect of the invention provides a method of operating a magnetic resonance imaging apparatus, the method including steps of: -cooling a magnet arrangement of the magnetic resonance imaging apparatus with at least one refrigerator having a movable displacer for displacing a cold gas; -compensating a magnetic field generated by the displacer by
generating a compensating magnetic field; and
-using the magnet arrangement and magnetic resonance detector means for generating an image of an object located within the magnetic resonance imaging apparatus.
The method of the invention actively compensates the disturbing magnetic field generated by the moving displacer of the refrigerator by applying a compensating magnetic field. The compensating magnetic field cancels out the magnetic field generated by the moving displacer in such a way that the magnetic resonance imaging process remains unaffected by its detrimental effect.
A second aspect of the invention provides a cryogenic refrigerator having a movable displacer for displacing a cold gas. The displacer comprises a magnetic material such as Holmillm Copper. According to the invention the refrigerator further includes detector means adapted to detect a position of the displacer and to provide a detector signal comprising an information on the detected position of the displacer.
The cryogenic refrigerator has an advantage in that the position of the displacer is known during operation of the cryogenic refrigerator thereby allowing for active compensation means to be applied. Such active compensation means may include a source of magnetisation that will generate a magnetic field having such a phase relation and polarity that it will cancel the magnetic field generated by the moving magnetised displacer. In order to apply the compensating magnetic field with the correct phase and polarity, the position of the displacer should be known.
A related aspect of the invention provides a cryogenic refrigerator having a movable displacer for displacing a cold gas and comprising a magnetic material. According to this aspect of the invention the refrigerator further includes compensation means adapted to generate a magnetic dipole moment for compensating a magnetic field generated by the displacer.
According to this aspect of the invention the refrigerator may comprise compensation means that generate a suitable magnetic field that cancels out the magnetic field generated by the magnetised displacer. While such compensation means may benefit from the presence of detection means as explained above, it is possible to compensate the magnetic field without detecting the position of the displacer. On the other hand, it is also possible to cancel out the magnetic field of the displacer of the cryogenic refrigerator without providing dedicated compensation means and merely relying on the known position of the displacer as will be pointed out below. Thus, the two related inventive aspects achieve the same inventive idea relying on different technical features, however, form part of the same invention that is to actively compensate a magnetic field generated by the displacer by generating an overlay magnetic field that will cancel out the disturbing magnetic field. The interrelation between the various aspects of the invention will be appreciated when contemplating this
disclosure in its entirety.
The compensation means of the cryogenic refrigerator may include a coil and a current source connected to the coil.
The coil may be adapted to provide a current to the coil in accordance with the magnetic field generated by the displacer. In a typical environment the coil should be able to generate a dipole moment of 0.04 Am2. An exemplary coil with a cross sectional area of 10 cm2 would require 40 Ampere turns. That is to say, if the coil has 10 turns, a current of a maximum of 4 Ampere will suffice to generate the required dipole moment. Thus, a relatively small coil and a low current may be used for compensating the magnetic field cf the displacer. Generally, a current with a predetermined waveform may be used, however, it is also possible to determine the required magnetic field and thus current by using sensory devices to measure the magnetic field of the displacer and to derive the required waveform of the current
from the measured magnetic field.
In an alternative embodiment of the inventive cryogenic refrigerator the compensation means may include a magnetic body and actuator means for moving the magnetic body in accordance with the magnetic field generated by the displacer. The magnetic body may comprise or consist of a material which may be magnetised such as steel.
A further aspect of the invention provides a cryogenic refrigerator arrangement including a plurality of oryogenic refrigerators. Each of the refrigerators has a movable displacer for displacing a cold gas and comprising a magnetic material. According to the invention the cryogenic refrigerator arrangement further includes synchronisation means adapted to synchronise respective movements of the displacers of the cryogenic refrigerators.
The cryogenic refrigerator arrangement synchronises the various displacers of the refrigerators in such a way that the magnetic fields generated by the displacers mutually cancel out each other. For example, in a cryogenic refrigerator arrangement including two cryogenic refrigerators the displacers may be synchronised to move in opposite directions such that the magnetic fields of the two cryogenic refrigerators have opposite polarities and thus cancel out each other. In this way a displacer of one refrigerator may act as a magnetic body for compensating the magnetic field as explained above when referring to a preferred embodiment of the previous inventive aspect.
Cryogenic refrigerators including detector means as set forth above are especially suitable for use in such cryogenic refrigerator arrangements because the synchronisation means may rely on the detected positions of the displacers in order to synchronise their movements. In the same way the cryogenic refrigerator arrangement may further comprise detector means for detecting a respective position of each of the displacers of the cryogenic refrigerators.
Preferably the cryogenic refrigerator arrangement includes N cryogenic refrigerators with N being a positive natural number greater than 1. The synchronisation means may be further adapted to synchronise the respective movements of the displacers in such a way that a phase difference of movement between each of the displacers and a corresponding remaining one of the displacers is substantially egual to 360 degrees divided by the number N. In this way three or more refrigerators may be combined.
Yet another aspect of the invention provides a magnetic resonance imaging apparatus including a magnet arrangement and at least one cryogenic refrigerator of the invention.
Preferably a first distance between the displacer of the at least one cryogenic refrigerator and the compensation means of the at least one cryogenic refrigerator is at least five times lower than a second distance between the at least one cryogenic refrigerator and a centre of the magnet arrangement. The closer the displacer and the compensation means are to each other with respect to their distance from the centre of the magnet arrangement, the better the cancellation effect of the respective magnetic fields will be.
Alternatively a magnetic resonance imaging apparatus may include a magnet arrangement and an inventive cryogenic refrigerator arrangement as set forth above. As above the refrigerators should be located close to each other. However, in some arrangements the refrigerators may be located at opposite sides of the MRT apparatus as will be shown for an exemplary embodiment of the invention illustrated below.
Brief Description of the Drawings
The invention will be better understood from the following drawings in which a preferred embodiment of the invention will be illustrated by way of example. In the drawings: Figure 1 shows a first embodiment of a magnetic resonance imaging apparatus; Figure 2 shows a second embodiment of a magnetic resonance imaging apparatus; Figure 3 shows a third embodiment of a magnetic resonance imaging apparatus; and Figure 4 shows an exemplary device that can be used as compensating means in a magnetic resonance imaging apparatus according to the invention.
Detailed Description of the Drawings
Figure 1 shows a first embodiment of a magnetic resonance imaging apparatus. The MRI apparatus includes a magnet arrangement 2 having a substantially tubular shape. An object to be examined may be placed in the volume enclosed by the magnet arrangement 2 and subjected to the strong magnetic fields used for MRI. Such strong magnetic fields can be generated using superconducting magnets. Sinoe superconducting materials only exhibit their superconducting property below a critical temperature which usually is less than 100 Kelvin, the superconducting magnet must be cooled.
For this purpose cryogenic refrigerators 1 are provided to cool the magnet arrangement 2 of the magnetic resonance imaging apparatus. Usually liquid helium cryogenic refrigerators are used even for superconducting materials having a critical temperature far higher than 4.2 Kelvin because the superconductivity of the material benefits from lower temperatures.
In the first embodiment of the magnetic resonance imaging apparatus two refrigerators 1 are arranged side by side on one side of the magnet arrangement 2. Preferably the two refrigerators 1 are of identical make such that the respective displacers of the refrigerators 1 have the same magnetic properties. According to one aspect of the invention the displacers will be synchronised in such a way that they move in phase opposition. Tn this way their respective magnetic fields will cancel out each other. The cancellation effect will improve with increasing distance from the refrigerators 1. Thus, the refrigerators 1 should be located in proximity to each other. However, as illustrated by Figure 2, it is also possible to arrange the refrigerators 1 in a symmetric manner, e.g. on opposite sides of the magnet arrangement 2. Figure 2 shows a second embodiment of a magnetic resonance imaging apparatus including two refrigerators 1 arranged in such a way.
Generally the invention is not limited to using two refrigerators 1. As has been pointed out before, a single refrigerator 1 may be used. Tn such a case the refrigerator 1 comprises compensation means for compensating the magnetic field generated by the displacer of the refrigerator 1. when a plurality of refrigerators 1 are present, the displacers may be synchronised in such a way that their respective magnetic fields cancel out each cther. Nonetheless, it is also possible to combine the two related inventive aspects and to arrange two or more refrigerators 1 including compensation means as illustrated in Figs. 1 through 3 to achieve an even better compensation effect. Furthermore, shields as proposed in the prior art may be used in combination with the invention.
Figure 3 shows a third embodiment of a magnetic resonance imaging apparatus including three refrigerators 1. In such a case the displacers of the refrigerators 1 are synchronised to have a phase difference of 360 / N = 120 degrees with N being the number of refrigerators or displacers in the arrangement. Using the same phase relation, an arbitrary number of refrigerators 1 may be used.
Figure 4 shows an exemplary device that can be used as compensating means in a magnetic resonance imaging apparatus according to the invention. A motor 3 functions as actuator means and rotates a shaft 6 and a crank 5 connected to the shaft 6. Preferably the motor 3 is a synchronous motor.
The device further includes a magnetic body 4 which consists of or comprises a quantity of magnetisable material, for example of a ferromagnetic or paramagnetic material. The magnetic body 4 is mounted on the crank 5 and thus rotates about the shaft 6 in a cyclic manner. The device of Figure 4 emulates the effect of the displacer of a cryogenic refrigerator moving up and down. By adjusting the phase of the movement of the magnetic body 4 about the shaft 6 to that of the displacer, the magnetic field generated by the displacer may be compensated. Preferably the length of the crank 5 corresponds to half that of the stroke of the displacer.
Although the invention has been shown and described with re- spect to exemplary embodiments thereof, various other chang-es, omissions, and additions in form and detail thereof may be made therein without departing from the spirit and scope of the invention.
While the invention has been described in connection with a preferred embodiment, it is not intended to limit the scope of the invention to the particular form set forth, but on the contrary, it is intended to cover such alternatives, modifi-cations, and equivalents as may be included within the scope of the invention as defined by the appended claims.

Claims (11)

  1. Claims 1. A method of operating a magnetic resonance imaging apparatus, the method including steps of: -cooling a magnet arrangement of the magnetic resonance imaging apparatus with at least one refrigerator having a movable displacer for displacing a cold gas; -compensating a magnetic field generated by the displacer bygenerating a compensating magnetic field; and-using the magnet arrangement and magnetic resonance detector means for generating an image of an object located within the magnetic resonance imaging apparatus.
  2. 2. A cryogenic refrigerator having a movable displacer for displacing a cold gas, the displacer comprising a magnetic material, characterised by detector means adapted to detect a position of the displacer and to provide a detector signal comprising an information on the detected position of the displacer.
  3. 3. A cryogenic refrigerator having a movable displacer for displacing a cold gas, the displacer comprising a magnetic material, characterised in that the refrigerator further includes compensation means adapted to generate a magnetic dipole moment for compensating a magnetic field generated by the displacer.
  4. 4. The cryogenic refrigerator of the preceding claim, wherein the compensation means include a coil and a current source connected to the coil and adapted to provide a current to the coil in accordance with the magnetic field generated by the displacer.
  5. 5. The cryogenic refrigerator of claim 3, wherein the compensation means include a magnetic body and actuator means for moving the magnetic body in accordance with the magneticfield generated by the displacer.
  6. 6. A cryogenic refrigerator arrangement including a plurality of cryogenic refrigerators each of which having a movable displacer for displacing a cold gas and comprising a magnetic material, characterised by synchronisation means adapted to synchronise respective mcvements of the displacers of the cryogenic refrigerators.
  7. 7. The cryogenic refrigerator arrangement of the preceding claim, including N cryogenic refrigerators and wherein the synchronisation means are further adapted to synchronise the respective movements of the displacers in such a way that a phase difference of movement between each of the displacers and a corresponding remaining one of the displacers is substantially egual to 360 degrees divided by the number N.
  8. 8. The cryogenic refrigerator arrangement of one of the claims 6 or 7, further comprising detector means for detecting a respective position of each of the displacers of the cryogenic refrigerators.
  9. 9. A magnetic resonance imaging apparatus including a magnet arrangement and at least one cryogenic refrigerator as claimed in one of the claims 3 through 5.
  10. 10. The magnetic rescnance imaging apparatus of the preceding claim, wherein a first distanoe between the displacer of the at least one cryogenic refrigerator and the compensation means of the at least one cryogenic refrigerator is at least five times lower than a second distance between the at least one cryogenic refrigerator and a centre of the magnet arrangement.
  11. 11. A magnetic resonance imaging apparatus including a magnet arrangement and a cryogenic refrigerator arrangement as claimed in one of the claims 6 through 8.Amendments to the claims have been made as follows: Claims 1. A cryogenic refrigerator arrangement including a plurality of N cryogenic refrigerators each of which having a movable displacer for displacing a cold gas and comprising a magnetic material, characterised by synchronisation means adapted to synohronise the respective movements of the displacers of the cryogenic refrigerators in such a way that a phase difference of movement between each of the displacers and a corresponding remaining one of the displacers is substantially egual to 360 degrees divided by the number N. 2. The cryogenic refrigerator arrangement of claim 1, further comprising detector means for detecting a respective position of each of the displacers of the cryogenic refrigerators.(\,J 3. A magnetic resonance imaging apparatus including a magnet arrangement and a cryogenic refrigerator arrangement as claimed in one of the claims
    1-2. (4
GB1403757.6A 2014-03-04 2014-03-04 Active compensation of magnetic field generated by a recondensing refrigerator Withdrawn GB2523762A (en)

Priority Applications (3)

Application Number Priority Date Filing Date Title
GB1403757.6A GB2523762A (en) 2014-03-04 2014-03-04 Active compensation of magnetic field generated by a recondensing refrigerator
PCT/EP2015/052868 WO2015132055A1 (en) 2014-03-04 2015-02-11 Active compensation of magnetic field distortion generated by a recondensing refrigerator
EP15705950.2A EP3114494A1 (en) 2014-03-04 2015-02-11 Active compensation of magnetic field distortion generated by a recondensing refrigerator

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
GB1403757.6A GB2523762A (en) 2014-03-04 2014-03-04 Active compensation of magnetic field generated by a recondensing refrigerator

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GB201403757D0 GB201403757D0 (en) 2014-04-16
GB2523762A true GB2523762A (en) 2015-09-09

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GB (1) GB2523762A (en)
WO (1) WO2015132055A1 (en)

Citations (12)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4535595A (en) * 1983-02-09 1985-08-20 Bruker Analytische Mebtechnik Gmbh Cooling device for a low temperature magnet system
JPH10165388A (en) * 1996-12-10 1998-06-23 Ge Yokogawa Medical Syst Ltd Method of generating magnetic field for mri, and mri device
EP0899576A1 (en) * 1997-08-01 1999-03-03 ITEL Telecomunicazioni S.r.l. Active system for compensation of magnetic field disturbances, particularly suitable for use with nuclear magnetic resonance tomography
US20010013778A1 (en) * 2000-02-10 2001-08-16 Hitachi Medical Corporation Magnetic resonance imaging apparatus
US20040045303A1 (en) * 2000-10-25 2004-03-11 Wei Chen Stirling refrigerating system and cooling chamber with the refrigerating system
US20050082994A1 (en) * 2001-12-14 2005-04-21 Songgang Qiu Active balance system and vibration balanced machine
US20050253583A1 (en) * 2004-05-11 2005-11-17 Bruker Biospin Gmbh Magnet system with shielded regenerator housing
US20080030193A1 (en) * 2006-07-31 2008-02-07 Mitsubishi Electric Corporation Superconducting magnet and MRI apparatus using the same
US20100301977A1 (en) * 2009-06-01 2010-12-02 Mitsubishi Electric Corporation Superconducting Magnet Device
US20110126554A1 (en) * 2008-05-21 2011-06-02 Brooks Automation Inc. Linear Drive Cryogenic Refrigerator
US20130154648A1 (en) * 2011-12-20 2013-06-20 General Electric Company System and apparatus for compensating for magnetic field distortion in an mri system
US20130157865A1 (en) * 2011-12-20 2013-06-20 General Electric Company System for magnetic field distortion compensation and method of making same

Family Cites Families (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR2139964B1 (en) * 1971-05-28 1977-12-23 Ishizaki Yoshihiro
US4584839A (en) * 1984-07-02 1986-04-29 Cvi Incorporated Multi-stage cryogenic refrigerators
US6201462B1 (en) * 1999-11-09 2001-03-13 General Electric Company Open superconductive magnet having a cryocooler coldhead
US8384387B1 (en) * 2008-02-14 2013-02-26 Fonar Corporation Magnetic resonance imaging apparatus
JP2013144099A (en) * 2011-12-12 2013-07-25 Toshiba Corp Magnetic resonance imaging apparatus

Patent Citations (12)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4535595A (en) * 1983-02-09 1985-08-20 Bruker Analytische Mebtechnik Gmbh Cooling device for a low temperature magnet system
JPH10165388A (en) * 1996-12-10 1998-06-23 Ge Yokogawa Medical Syst Ltd Method of generating magnetic field for mri, and mri device
EP0899576A1 (en) * 1997-08-01 1999-03-03 ITEL Telecomunicazioni S.r.l. Active system for compensation of magnetic field disturbances, particularly suitable for use with nuclear magnetic resonance tomography
US20010013778A1 (en) * 2000-02-10 2001-08-16 Hitachi Medical Corporation Magnetic resonance imaging apparatus
US20040045303A1 (en) * 2000-10-25 2004-03-11 Wei Chen Stirling refrigerating system and cooling chamber with the refrigerating system
US20050082994A1 (en) * 2001-12-14 2005-04-21 Songgang Qiu Active balance system and vibration balanced machine
US20050253583A1 (en) * 2004-05-11 2005-11-17 Bruker Biospin Gmbh Magnet system with shielded regenerator housing
US20080030193A1 (en) * 2006-07-31 2008-02-07 Mitsubishi Electric Corporation Superconducting magnet and MRI apparatus using the same
US20110126554A1 (en) * 2008-05-21 2011-06-02 Brooks Automation Inc. Linear Drive Cryogenic Refrigerator
US20100301977A1 (en) * 2009-06-01 2010-12-02 Mitsubishi Electric Corporation Superconducting Magnet Device
US20130154648A1 (en) * 2011-12-20 2013-06-20 General Electric Company System and apparatus for compensating for magnetic field distortion in an mri system
US20130157865A1 (en) * 2011-12-20 2013-06-20 General Electric Company System for magnetic field distortion compensation and method of making same

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